Gun platform stabilization system



June 4, 1968 F. s. PRESTON 3,386,335

GUN PLATFORM STABILIZATION SYSTEM Filed June 6, 1967 2 Sheets$heet 1LINE OF FIRE LINE OF FIRE A/OPMQL L'NEOFFRE 7 To PITCH RXIS msmrucsNOPMAL To POLL Fix/5 D/STfl/VCE Hen/4L LINE or FIRE FIROUND P/rcH Hx/s/O AcruqL LIA/E OF F/PE GEO/VD POLL 4x15 INVENTOR.

Bank 5. Pre57o 7 Q T TOPNEYS United States Patent 3,386,335 GUN PLATFORMSTABILIZATION SYSTEM Frank S. Preston, Fairfield, Comm, assignor toUnited Aircraft Corporation, East Hartford, Conn., a corporation ofDelaware Filed June 8, 1967, Ser. No. 644,628 15 Claims. (Cl. 8941)ABSTRACT OF THE DHSCLOSURE Background of the invention It is well knownthat a gun supported on a movable platform or vehicle reacts thereon.Systems are known in the prior art for stabilizing the platform tocorrect for changes in attitude resulting from external influences. Inaddition to these external influences, there exists the force ofreaction on the platform resulting from firing of the gun. Where theplatform or vehicle has a relatively large mass, these reaction forcescan be absorbed by various systems such, for example, as a carriage andspring arrangement or by venting gas from the gun barrel.

In some instances, however, the stabilizing arrangements described aboveare entirely unsuitable. For example, a helicopter or a satellite makesa very poor gun platform in that the reaction force tends to swing theplatform unless the reaction force is directed through the center ofgravity. While the pilot or some automatic attitude stabilizing systemcan restore the platform to its initial attitude following a change inattitude resulting from firing, this operation takes appreciable time ascompared with the time during which a gun firing at a very rapid rate isfired in short bursts. These factors have resulted in a limitation ofthe permissible rate of fire consistent with accuracy or they haveresulted in inaccurate firing.

I have invented a gun platform stabilization system which, in a rapidand expeditious manner, counteracts the platform torque resulting fromfiring of a gun. My system permits a gun to be fired at a relativelyrapid rate with greater accuracy than is possible with systems of theprior art. My arrangement is simple for the result achieved thereby.

Summary of the invention One object of my invention is to provide a gunplatform stabilization system which acts in a rapid and expeditiousmanner to counteract the torque exerted on the platform by firing of thegun.

Another object of my invention is to provide a gun platformstabilization system which permits a gun on a relatively light platformto be fired rapidly with a relatively high degree of accuracy.

A further object of my invention is to provide a gun platformstabilization system which is simple in its construction and in itsoperation for the result achieved thereby.

Other and further objects of my invention will appear from the followingdescription.

In general my invention contemplates the provision of a gun platformstabilization system in which, in .response to firing of the gun, Igenerate a signal which is an approximate measure of the torque exertedon the platform as a result of the firing. I apply the torque signal toa "ice device adapted to apply a torque to the platform, which torque isgenerally equal and opposite to the disturbing torque resulting fromfiring of the gun.

Brief description of the drawings In the accompanying drawings whichform part of the instant specification and which are to be read inconjunction therewith and in which like reference numerals are used toindicate like parts in the various views:

FIGURE 1 is a diagrammatic view of a gun and platform to which I mayapply my platform stabilizing system.

FIGURE 2 is a diagram illustrating the effect of firing of the gun ontwo mutually perpendicular axes.

FIGURE 3 is a schematic view illustrating one form of my gun platformstabilizing system.

FIGURE 4 is a schematic view of another form of my gun platformstabilizing system.

Description 0 the preferred embodiment Referring now to FIGURE 1 of thedrawings, I have shown a platform 19 which may, for example, be a lightvehicle, such as a helicopter or a satellite or the like, which carriesa gun mount 12 supported for pivotal movement around an axis 14 spacedat a distance d from an axis passing through the center of gravity 16 ofthe platform 10. By way of example, I have illustrated the direction ofmovement of the platform 10 by the arrow V on the broken line 20 passingthrough the center of gravity 16. With the gun 18 oriented at an angle4) to the line 20, when the gun is fired there results a reaction forceF acting on the platform 10 through an arm I. This action produces atorque T tending to rotate the platform 10 around the center of gravity16 so that (l) T=Fl The force F can be expressed as some constant ktimes the rate of change of momentum M or F==kdM/dt The rate of changeof momentum is approximately equal to the product of the mass m of around times the rate of fire r so that we can write It can readily beseen that the length of arm I is given by the product of the distance dbetween the gun pivot and the center of gravity times the cosine of theangle between the gun barrel l8 and the direction of movement of thecraft. Thus I generate a torque equal and opposite to the torquerepresented by Equation 4 to counteract the effect of firing of the gunon the platform 10.

Referring to FIGURE 2, by way of example I have shown an arbitrary lineof fire in space by the large arrow with the gun pivot spaced from theintersection of the roll and pitch axes at the center of gravity of thesystem. Considering only the elfect on the roll and pitch axes, I firstprojected the space line of fire onto a plane in which the pitch axislies and onto a plane in which the roll axis lies. Taking first the rollaxis, we know that the maximum torque around the roll axis will resultif the line of fire is normal to a line representing the distance d fromthe center of gravity to the projected gun pivot. I have representedsuch a line of fire by the dot-dash line in the figure. The projectionof the actual line of fire, however, is not normal to the distance d butmakes an angle b,. with the normal. It will be clear from theexplanation hereinabove that a normal l to the projection of the actualline of fire is l =d cos o Knowing this distance we can generate thesignal representing the com- T=kmrd cos p ponent of torque around theroll axis in the manner de scribed above. The component of torque aroundthe pitch axis may be arrived at in a similar manner.

Referring to FIGURE 3, I have shown one form of my compensating systemwhich acts around one axis of the platform 10. I apply a signal e=E sinat at a terminal 22 to an autotransformer winding 24. The transformerpickoff 26 is adapted to be positioned either manually or in response toa suitable computer through a linkage 28. I so position the pickoff 26as to provide a signal e =E sin wt on a conductor 30 where E =kmrdE.

The system shown in FIGURE 3 includes a resolver indicated generally bythe reference character 32 having a rotor winding 34 and respectivestator windings 36 and 38, the latter winding not being employed in mysystem. I provide a mechanical coupling, indicated by the broken line40, between the movable mount 12 and the rotor 34 of the resolver 32 tocause the resolver winding 32 to be positioned from a referencedirection in accordance with the angle between the gun barrel 18 and theline 20 of movement of the platform. I also connect conductor 30 to thewinding 34. I so select the reference direction that the angle 4 withrespect to a particular axis is the angle between the line producingmaximum torque around that axis and the actual line of fire referred tothat axis.

From the structure just described it will be appreciated that winding 36carries an output signal k E cos sin wt. It will further be apparentthat this signal is an analog of the torque exerted on the plat-formaround a vertical axis as viewed in FIGURE 3 as a result of firing ofthe gun. A normally open switch 42 which, preferably, is closed inresponse to operation of the gun trigger couples the signal on winding36 to an amplifier 44 which supplies the torque compensating unitindicated generally by the reference character 46 of my system.

It is to be understood that I may employ any suitable arrangement 46 forapplying the counteracting torque in response to the signal on winding36. By way of example, I have schematically shown a reaction wheelincluding a stationary armature 48 and a movable wheel 50 supported formovement around an axis 52 on the vehicle. Wheel 50 carries means such,for example, as permanent magnets (not shown) which interact with thefield resulting from energization of the armature 4 8 to tend to rotatethe wheel. The resulting force provides a reaction torque on the vehicleor platform 10. Preferably wheel 50 is mounted for movement around thataxis, passing through the center of gravity, around which compensationis desired. Alternatively, it may be mounted for movement around an axisparallel to the axis around which compensation is desired,

Alternative to the particular torque compensating unit 46 shown, I mayemploy other arrangements such, for example, as the inertial compensatorillustrated in FIG- URES 6 to 14 of Patent No. 3,039,096. Still anotherarrangement might be one wherein an autopilot or autostabilizer wasactuated to operate through the normal controls of the vehicle.

Referring now to FIGURE 4, by way of a further example I have shown themount 12 supported on a helicopter 54. As in the form of the systemshown in FIGURE 3, the linkage 40 drives the rotor 34 of the resolver 32in response to movement of the mount 12. In this arrangement a knob 56can be operated to set the rate of fire by moving a brush 58 along apotentiometer winding 60 which is supplied with the signal e=E sin wtfrom a terminal 62. It will readily be appreciated that a signalcorresponding to that produced by setting knob 56 might be generatedautomatically by the gun. Brush 58 applies the signal kmre to anoperational amplifier 64 which feeds the potentiometer winding 66.

The helicopter 54 includes a pilots control lever 68 supported on ashaft 70 and normally centered by springs 72 and 74 carried by the feeldatum trim unit 76. A linkage 78 responsive to the lever 68 positionsthe brush 80 associated with winding 66 as determined by the trimmeddatum position of the feel system which, as is known in the art, isproportional to the center of gravity position. Owing to thisarrangement, a conductor 82 connected to brush 80 carries the signalkmrd. An operational amplifier 84 couples the signal kmrd to the rotorwinding 34 of resolver 32 to cause the winding 36 to provide the signalkmrd cos sin wt.

A link 86 connects the control lever 68 to a lever 88 coupled by a link96 to a lever 92 carrying a link 94 adapted to operate a power control96 for operating a swash plate and driver mix mechanism 98 having anoutput shaft 100 driving a linkage 102 for positioning the controlledmember 104. Since this structure is well known in the art, it will notbe described in further detail.

I provide my system with a stabilizer actuator servo loop 106 includingan amplifier 108 which supplies a motor 116 to drive a shaft 112carrying a inion 114 which drives a gear 116 for driving a worm 118 toposition the brush 120 of a follow-up potentiometer 122 providing oneinput to the amplifier 108. The arrangement incorporates a linkage 124providing an input to a gyro reference 126 supplying an output signal asanother input to amplifier 108, which output is a measure of the actualposition of the controlled member 104. A tachometer 128 driven by shaft112 provides a rate input to amplifier 108. I connect the trigger switch42 to provide the fourth input to the amplifier 108. In this way theautomatic stabilizer actuator provides such a control of the surface 104as to give rise to a torque for compensating the effect of firing of thegun 18.

It is to be understood that except for the input provided by operationof switch 42, the stabilizer actuator servo loop 106 is well known inthe art. For that reason, it will not be described in detail. For thepurposes of my invention, it is to be understood only that with theinput provided by operation of switch 42 when the gun is fired, thesystem including the loop 106 functions to apply such a torque' to thehelicopter around the axis under consideration as will compensate forthe torque around that axis resulting from firing of the gun. As hasbeen explained hereinabove, my arrangement is not limited to aparticular axis but may readily be applied around any axis for whichcompensation is necessary or desirable. In such a system I use anindividual resolver 32 for each of the axes around which compensation isdesired. Where I generate a number of signals corresponding to thecompensating torques required with reference to the various axes, I usea multiple axis control system to which I feed these signals. By way ofexample, I may employ a control system such as is shown and described inUnited States Patent No. 3,071,335.

In operation of the form of my arrangement shown in FIGURE 3, forexample, where a gun 18 is mounted for pivotal movement around avertical axis spaced a distance d from a vertical axis passing throughthe center of gravity, the maximum torque around that axis resultingfrom firing of the gun 18 will occur when the gun is aligned with thevector V shown in the figure. In such case, the output of resolverwinding 36 will be E sin wt where E is equal to kmrd since cos =l. Ifnow the line of fire changes or has to be at an angle with respect to aline parallel to the vector V, then the signal output from Winding 36will be E wt cos a5 where cos 4: is less than 1. Stated otherwise, withthe actual line of fire at an angle to the line corresponding to maximumtorque, the .force is acting through a moment arm I which is less thanthe distance d and which is l=d cos The rate of fire can readily be setby moving the brush along the autotransformer winding 24. It willreadily be understood that this also might be under the control of thefiring of the gun. The manner in which my system can 7 be adapted to aplurality of axes will readily be understood from the showing of FIGURE2.

In operation of the form of my system shown in FIG- URE 4, the rate offire is set by actuating knob 56 to set brush 58 manually on theresistor 60 or the same resultant signal may be generated automatically.Movement of brush 80 on resistor 66 compensates this system for changesin the center of gravity. With the resultant signal applied to winding34, then winding 36 produces the si.,- nal km rd sin wt cos 1: which isapplied by the trigger responsive switch 42 as one input to the loop 106which, in a manner known to the art, causes the compensating torque tobe applied to the craft. Where a multiple axis system is employed, acontrol system adapted to receive inputs corresponding to the respectiveaxes is used.

It will be seen that I have accomplished the objects of my invention. Ihave provided a gun platform stabilization system for rapidly andexpeditiously counteracting the torque exerted on the gun platform as aresult of firing the gun. My invention permits a gun mounted on arelatively light platform to be fired rapidly with a relatively highdegree of accuracy. My system is simple in construction and operationfor the result achieved thereby. It will be understood that certainfeatures and subcom binations are of utility and may be employed withoutreference to other features and su-bcombinations. This is contemplatedby and is within the scope of my claims. It is further; obvious thatvarious changes may be made in details within the scope of my claimswithout departing from the spirit of my invention. It is, therefore, tobe understood that my invention is not to be limited to the specificdetails shown and described.

Having thus described my invention, what I claim is:

1. A system for stabilizing a platform with reference to an axisthereof, said platform carrying a gun mounted for movement at a locationspaced from said axis to establish a movable line of fire, including incombination, means responsive to firing of said gun for generating asignal representing a disturbing torque applied to said platform aroundsaid axis owing to said firing and means responsive to said signal forapplying a compensating torque to said platform around said axis tocounteract the effect of said disturbing torque.

2. A system as in claim :1 in which said signal generating meanscomprises means for producing a signal representing the maximum torqueresulting from a line of fire of said gun normal to a line from saidlocation to said axis and means responsive to deviation of the actualline of fire from said normal line of fire for modifying said maximumtorque signal to provide said disturbing torque signal.

13. A system as in claim v1 in which said signal generating meanscomprises means for producing a signal proportional to the product ofthe mass of a round fired by said gun and the rate of fire of said gun.

4. A system as in claim 1 in which said signal generating meanscomprises a variable transformer having a fixed winding and a movablewinding and means responsive to movement of said movable line of firefor moving said movable .winding.

5. A system as in claim 1 in which said signal generating meanscomprises a resolver having a rotor winding and a stator winding, meansresponsive to movement of said line of fire for driving said rotorwinding, means for producing a signal representing the maximum torqueresulting from a line of fire of said gun normal to a line from saidlocation to said axis and means for applying said maximum torque signalto said rotor winding.

6. -A system as in claim 1 in which said signal generating meanscomprises .a resolver having a rotor winding and a stator cosinewinding, means responsive to movement of said line of fire for drivingsaid rotor winding, means for producing a signal representing themaximum torque resulting from a line of fire of said gun normal to aline from said location to said axis and means for applying said maximumtorque signal to said rotor windmg.

7. A system as in claim 1 in which said signal generating meanscomprises a variable transformer having a fixed winding and a movablewinding, means for producing a signal proportional to the product of therate of fire of said gun and the mass of a round fired by said gun,means for applying said product signal to one of said windings and meansresponsive to movement of said line of fire for driving said movablewinding to cause the other winding to provide said disturbing torquesignal.

8. A system as in claim 1 in which said compensating torque applyingmeans includes a normally open switch adapted to be closed concomitantlywith the firing of the gun.

9. A system as in claim 1 in which said compensating torque applyingmeans comprises an electromagnetic reaction device having a pair ofmembers, means mounting one of said members on said platform formovement therewith, means mounting the other member on said platform forrotary movement with respect to the other member, one of said membersbeing energizable to generate a reaction between said members and meansfor applying said signal to said energizable member.

10. A system as in claim 1 in which said compensating torque applyingmeans comprises a control surface coupled to said platform, a servo loopfor actuating said control surface and means for coupling said signal tosaid servo loop as one input thereto.

illl. A system as in claim 1 in which said compensating torque applyingmeans comprises means for generating a signal representing the productof the force resulting from firing of said gun and the distance fromsaid gun mount to the center of gravity of said platform, a feel datumtrim unit and means responsive to said unit for modifying said productsignal to compensate for changes in the center of gravity of saidplatform.

12. A system as in claim 1 in which said signal producing meanscomprises a resolver having a rotor winding and a cosine stat-orwinding, means for producing a signal proportional to the product of themass of a round [fired by said gun and the rate of fire of said gun andthe distance of the gun mount from the center of gravity of saidplatform, means for applying said product signal to said rotor winding,means responsive to movement of said line of fire for moving said rotorwinding to cause said stator winding to provide said disturbing torquesignal and a normally open switch actuatable concomitantly with thefiring of the gun for applying said disturbing torque signal to saidcompensating torque applying means.

13. A system as in claim 1 in which said signal producing meanscomprises a resolver having a rotor winding and a cosine stator winding,means for producing a signal proportional to the product of the mass ofa round fired by said gun and the rate of fire of said gun and thedistance of the gun mount from the center of gravity of said platform,means for applying said product signal to said rotor winding, meansresponsive to movement of said line of fire for moving said rotorwinding to cause said stator winding to provide said disturbing torquesignal, and in which said compensating torque applying means is anelectromagnetic reaction device comprising a pair of relatively movablemembers, means mounting one of said members on said platform formovement therewith, one of said members being energizable to generate areaction torque between said members and a normally open switchactuatable concomitantly with the firing of the gun for applying saiddisturbing torque signal to said compensating torque applying means.

14. A system as in claim 1 in which said signal producing meanscomprises a resolver having a rotor winding and a cosine stator winding,means for producing a signal proportional to the product of the mass ofa round fired by said gun and the rate of fire of said gun and thedistance of the un mount from the center of gravity of said platform,means for applying said product signal to said rotor winding, meansresponsive to movement of said line of fire for moving said rotorwinding to cause said stator winding to provide said disturbing torquesignal, and in which said compensating torque applying means is anelectromagnetic reaction device comprising a pair of members relativelymovable around said axis, means mounting one of said members on saidplatform for movement therewith, one of said members being energizableto generate a reaction torque between said members and a normally openswitch actuatable concomitantly with the firing of the gun for applyingsaid disturbing torque signal to said compensating torque applyingmeans.

15. A system as in claim 1 in which said signal producing meanscomprises a resolver having a rotor winding and a cosine stator winding,means for producing a signal proportional to the product of the mass ofa round fired by said gun and the rate of fire of said gun and thedistance of the gun mount from the center of gravity of said platform,means for applying said product signal to said rotor winding, meansresponsive to movement of said line of fire for moving said rotorwinding to cause said stator winding to provide said disturbing torquesignal, and in which said compensating torque applying means comprises acontrol surface adapted to be actuated to apply a torque to saidplatform, means including a servo loop for actuating said surface, afeel datum trim unit, means responsive to said feel datum trim unit formodifying said product signal to compensate for changes in the center ofgravity of said platform and a normally open switch actuatableconcomitantly with the firing 0f the gun for applying said disturbingtorque signal to said compensating torque applying means.

BENJAMIN A. BORCHELT, Primary Examiner.

T. H. WEBB, Assistant Examiner.

